Synthesis of Aqueous Ferrofluid
Adapted by Megan L. Kunz and Thomas. C. Keane, Ph.D
Purpose:
The object of this module is to observe the properties of a ferrofluid in the
presence of an external magnetic field.
Learning Objectives
1) Recognize and explain the effects that a magnetic field has on paramagnetic
materials
2) Demonstrate understanding of electron configurations
3) Explain the effects of a molecule’s dipole interactions on aggregation
Introduction:
Ferrofluids are colloidal suspensions of magnetic nanoparticles. A colloidal
suspension is a suspension of a particle that is so small that it doesn’t settle out of
solution rapidly, even in the presence of gravity. Ferrofluids can respond distinctly to
magnetic fields. A magnetic field is created by the movement of electrons. Most
magnetic fields are dipolar in nature and a have a positive and negative field. In an atom
the magnetic field is created by the movement of electrons and the spins of the electrons
in the atom.
The response of the ferrofluid to the magnetic field is due to the electron
configuration of the material contained in the ferrofluid. Aqueous Ferrofluid can be
produced by mixing Fe(II) and Fe(III) salts together, forming Fe3O4. Fe (II) and Fe(III)
are both paramagnetic materials that contain unpaired d electrons. The unpaired electrons
are what cause the paramagnetic field. There is another type of field which is called
diamagnetic. To some extent all materials have a form of a diamagnetic field. The
interaction of the diamagnetic field is weak in comparison to the strength of the
paramagnetic field. Materials in a paramagnetic field are attracted to the magnetic field,
whereas in a diamagnetic field the materials are repelled by the magnetic field. Therefore
since the Fe3O4 is paramagnetic there is an attracted force which is stronger than the
repelling force created by the diamagnetic field. The paramagnetic field is due to the
electron spin configuration of the unpaired electrons. According to Hund’s rule if there
are unpaired electrons they must have parallel spins. The electron spin of the electrons
create the magnetic properties. The unpaired electrons with the parallel spins create the
magnetic field. Paired electrons are said to have opposite spins.
Because the ferrofluid is in a colloidal suspension, there is a dipolar interaction
that occurs between the ferrofluid and the liquid medium. This dipole interaction is
created by the solution tetramethylammonium hydroxide. The polar end of the medium is
attracted to the iron from ion-dipole forces. The dipole interaction is what keeps the
nanoparticles from aggregating in the solution.
When an external magnetic field is applied to the ferrofluid and spikes are
observed.
Materials:
2M HCl
2.0 M FeCl2 (H2O)4
1.0 M FeCl3(H2O)6
1.0 M NH3 in water
25% tetramethylammonium hydroxide in water.
Cow magnetic
Wash bottles
Gloves (a must, ferrofluid will stain hands)
Stir bar and magnetic stirrer
Separatory funnel
Procedure:
1)
2)
3)
4)
5)
6)
7)
8)
9)
Set up a magnetic stirrer on a ring stand in a fume hood.
Then set up a separatory funnel or burette above the
magnetic stirrer. As shown to the left.
In a 100 ml beaker add 4.0 ml of 1M FeCl3 solution and 1.0
ml of 2M FeCl2 solution. Add a magnetic stir bar and begin
stirring.
Place 50 ml of aqueous 1.0 M NH3 into the separatory
funnel. With continuous stirring add the 1M aqueous NH3
dropwise over a five minute period. (There will first be a
brown precipitate that forms and then the solution will form
black magnetic precipitate). CAUTION: NH3 is a strong
base even though it is dilute.
Immediately turn off the stirrer after all of the NH3 is
added.
Then using a strong magnet work the stir bar up the side of
the container then with gloves or thongs remove the stir bar
from the beaker.
Allow the magnetite to settle to the bottom of the beaker.
Use a strong magnet at the bottom of the beaker to speed up
the process.
Once the magnetite is at the bottom of the beaker, decant
(pour off) the clear liquid. To aid in keeping the remainder
of the magnetite in the bottom of the beaker, keep the cow
magnet on the bottom of the beaker while pouring off the
liquid.
With a few squirts from a wash bottle of dH2O transfer the
solid into a plastic weigh boat.
Use the magnet to attract the ferrofluid to the bottom of the
weigh boat and discard the clear liquid. Rinse the ferrofluid
three times with water. Using the same decanting
technique. Do not remove all of the water, because a solid
will form.
10)
11)
12)
13)
Once the washing is finished add, with a pasture pipette, 12ml of 25 % tetramethylammonium hydroxide.
Gently stir the solution with a glass rod for at least a minute
to suspend the ferrofluid.
Use a strong magnet to attract the ferrofluid to the bottom
of the weigh boat and pour off and discard the dark liquid.
Move the magnet around again and pour off any liquid.
Repeat this process continually until the ferrofluid starts to
spike in the presence of the magnet.
Discussions:
1) Write out the electron configuration for the Fe(II) and Fe(III) ions. Also write out the
orbital diagram to show the unpaired electrons using the high spin case along with
Hund’s rule.
2) Describe what happens when the ferrofluid is in the presence of the magnet, and also
what happens when the magnet is removed.
3) Explain in your own words, on a molecular level, why the observations in question 2
occurred.
4) Explain the purpose of adding the NH3 dropwise, speculate on what might occur if the
NH3 was added all at once.
5) What is the purpose of the tetramethylammonium hydroxide in the reaction?
6) Balance the following chemical reaction
__ FeCl3 + __ FeCl2 + __ NH3 + __ H2O → __ Fe3O4 + __ NH4Cl
7) According to the balanced reaction which ion is in the greatest supply in the Fe3O4:
Fe (II) or Fe (III).
Citations
Lisensky, G ( 2007, September, 25). Synthesis of Aqueous Ferrofluid. Interdisciplinary
Education Group, Retrieved March 6, 2008, from
http://mrsec.wisc.edu/Edetc/nanolab/ffexp/index.html.
American Chemical Society, (1998). Ferrofluid. Chemistry comes alive , Retrieved April
15, 2008, from
http://jchemed.chem.wisc.edu/jcesoft/cca/cca2/MAIN/FEFLUID/CD2R1.HTM
Tolbert, Sarah (2007). How to Make a Ferrofluid. UCLA, Retrieved April 15, 2008, from
http://voh.chem.ucla.edu/classes/Magnetic_fluids/pdf/Ferrofluid%20Student%20
Manual%202005.doc
1) Write out the electron configuration for iron metal and the Fe(II) and Fe(III) ions. Also
write out the orbital diagram to show the unpaired electrons using the high spin case
along with Hund’s rule.
Fe
Fe II
Fe III
[Ar].3d6.4s2
[Ar].3d6
[Ar].3d5
1s2 2s22p63s23p64s03d5
1s2 2s22p63s23p64s03d5
•
1s2 2s2p6 3s2p6d6 4s2
2) Describe what happens when the ferrofluid is in the presence of the magnet, and also
what happens when the magnet is removed.
When the magnet is applied the ferrofluid forms spikes, when it is removed it goes back
to liquid.
3) Explain in your own words, on a molecular level, why the observations in question 2
occurred.
Because of the unpaired electrons in the sample, the ferrofluid is paramagnetic which
means it is attracted to a magnetic field. When the magnet is applied the spins align and
they cause the liquid to spike and be attracted to the surface of the magnet.
4) Explain the purpose of adding the NH3 dropwise, speculate on what might occur if the
NH3 was added all at once.
The substance would aggregate together and clump. The substance would folliculate.
5) What is the purpose of the tetramethylammonium hydroxide in the reaction?
The tetramethyl ammonium hydroxide in the reaction serves to is that it create a dipole
interaction with the iron molecules and it keeps the molecules from aggregating.
6) Balance the following chemical reaction
_2_ FeCl3 + _1_ FeCl2 + _8_ NH3 + _4_ H2O → _1_ Fe3O4 + _8_ NH4Cl
7) According to the balanced reaction which ion is in the greatest supply in the Fe3O4:
Fe (II) or Fe (III).
Fe (III)
Pre-lab Materials
Preparation of FeCl2(H2O)4 solution
Dissolve 19.9 grams of FeCl2(H2O)4 in 50 ml of 2M HCl.
Preparation of FeCl3(H2O)6 solution
Dissolve 54.1 grams of FeCl3(H2O)6 in 200 ml of 2M HCl.